Which phrase best defines a biome? A. an interacting community of different species
B. a community and its abiotic factors
C. a large area dominated by specific kinds of organisms
D. a group of individuals of the same species

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

layer 3 is younger than layer 6.